The proposed research project is designed to investigate the processing of complex auditory signals. The project contains three parts: human psychoacoustics, animal psychophysics and electrophysiology. The primary stimuli are complex sounds with rippled amplitude spectra. a chinchilla will be used for the animal psychophysical and electrophysiological work. Spectrally rippled stimuli relate to a large array of auditory phenomena including: pitch perception, frequency selectivity, temporal processing, echo or reflection processing, and suppression or inhibition. The human psychophysical studies will concentrate on comparing pitch attributes across the various pitch producing stimuli, will explore the relationship between pitch and reflection processing, and will investigate the temporal and binaural attributes of processing spectrally rippled stimuli. Because of the research team's past behavioral and physiological work with a simple organism's responsiveness to rippled stimuli and because of the large body of relevant psychophysical literature, the proposal seeks to begin an understanding of the physiological mechanisms that unerlie the processing of these complex signals. Such a physiological study will be conducted in concert with animal psychophysical studies attempting to determine the sensitivity of the animal to these complex signals. Spectrally rippled signals with their many similarities to real world stimuli make them valuable stimuli for probing auditory processing of complex stimuli.